Epidermal keratinocytes are held together by intercellular junctions called desmosomes, which are critical for the maintenance of cell-cell adhesion, tissue integrity, and organ function. Desmogleins (Dsg) are the transmembrane adhesive components of the desmosomes. In the epidermis, Dsg2 and Dsg3 are expressed in the proliferative basal keratinocytes while Dsgl is expressed in the upper differentiated cells. There is compelling evidence that desmogleins mediate cell-cell adhesion. In the human autoimmune blistering disease pemphigus, antibodies directed against Dsg1 and Dsg3 induce blister formation in the epidermis and oral mucosa. In mouse, ablation of the Dsg3 gene results in blister formation similar to that observed in pemphigus vulgaris. However, forced expression of Dsg3 in superficial epidermis where Dsg1 is expressed prevents blister formation by pemphigus foliaceus anti-Dsg1 antibodies. These data demonstrate that Dsg1 and Dsg3 play a pivotal role in epithelial cell adhesion and that one desmoglein can compensate the loss of another. The role of Dsg2 in the epidermis remains elusive in part due to its weak expression. The overall goal of this project is to elucidate the function of Dsg2 in cell adhesion in the skin. The following specific aims are proposed: 1) demonstration of pathogenic pemphigus antibodies that recognize unique epitopes on Dsg2, 2) disruption of the normal expression of Dsg2 in the epidermis, and 3) determining whether Dsg2 can compensate for the loss of Dsg1 and Dsg3. To achieve these specific aims, GST-fusion proteins of the extracellular domains of Dsg2,A,ill be used to characterize pemphigus sera by immunoblotting analysis. In addition, affinity purified Dsg2-specific pemphigus antibodies will be tested to determine specificity in relation to Dsg1 and Dsg3. Dsg2-adsorbed pemphigus antibodies will be tested by passive transfer assays for pathogenicity in neonatal mice. The function of Dsg2 in the epidermis will be studied using transgenic mice expressing Dsg2 in the superficial epidermis under control of the involucrin promoter, which has activity in cells undergoing differentiation. Such mice would provide valuable insights into the biological function of Dsg2 in the development of a functional epidermis with respect to cellular proliferation, differentiation, adhesion and bar-her functions. Finally passive transfer studies will be performed with pemphigus IgG to determine if Dsg2 can protect against anti-Dsg1 -and/or anti -Dsg3 -induced cellular acantholysis. To this end, the ultimate goal is to find a means to upregulate Dsg2 in the epidermis as a therapeutic approach to pemphigus.